Composite set



June 21, 1938. EA. CQ AN 2,121,287

COMPOSITE SET Filed March 3, 1937 LINE TE L [PHONE FIG. 2

TELEPHONE LINE -1 U- TELEGRAPH NETWORK 2 FIG. 3

W LINE TELEGRAPH C 2: ==c c:, 2::(

2 W }BALA/VC/NG TELEPHONE W W NE T ORK /N VEN TOR By FA .COWA N A7'TORNEV Patented June 21 1938 UNITED STATES PATENT OFFICE COBIPOSITESET Apflication March 3, 1937, Serial No. 128,839

3 Claims.

This invention relates to multiplex signaling systems and moreparticularly to improvements in arrangements, such as composite sets,usually associated with the terminal facilities of the lines of suchsystems to prevent the different currents utilized from interfering witheach other:

An object of the invention is to permit the interconnection of twocommunication circuits, employing currents of difierent frequencies,with a common transmission line, so that both balance and frequencydescriminatlon .will be established between said circuits, and betweenthe transmission line and the balancing network of the composite set,and frequency discrimination will be provided. between -eachcommunication circuit and the balancing network whereby energydissipation in the balancing network will be reduced.

In common with other composite sets it is the function of the compositeset of this invention to permit the simultaneous use of both telephoneand telegraph facilities or the like over a common system oftransmission lines, to permit the separation of the telephone andtelegraph currents at terminals and to prevent interference between thecurrents of these facilities. The composite set of.this invention makesuse of the well-known combined balance and frequency discriminationwhich may be obtained by a Wheatstone bridge employing reactiveelements.

The composite set of this invention is similar to that shown anddescribed in United States Patent 1,681,216 issued August 21, 1928 to D.E. Branson and R. B. Shanck, except that by a rearrangement of theelements of the bridge circuit the set of this invention tends toexclude both the telephone and telegraph currents from the balancingnetwork. In the composite set of the above patent approximately half theenergy of both telephone and telegraph transmission is dissipated in thebalancing network.

The invention may be more fully understood from the followingdescription together with the accompanying drawing in Figs. 1, 2 and' 3of which the invention is illustrated:

Figure 1 shows a circuit diagram embodying a preferred form of theinvention.

Fig. 2 shows in diagrammatic form the composite set of this invention;and

Fig. 3' shows in schematic form the bridge 50. circuit employed.

In Fig. 1 is shown a line circuit connected through condenser C4 to atelephone circuit and through retardation coils L1 to a pair oftelegraph legs. Condensers C1 shunted across the telegraph circuit andprovided with a midpoint ground assist in suppressing noise from thetelegraph circuit which might produce cross-talk into the telephonecircuit. Condensers C4 serve to exclude telegraph currents from thetelephone circuit and coils L1 serve to exclude telephone 5 currentsfrom the telegraph circuit. Coils L2 and condensers C3 are then added asindicated to provide balancing arms for a Wheatstone bridge and networkI is added to simulate and balance the line impedance. The functions ofthese ele- 19 merits may be more readily perceived in Figs. 2 and 3. Itis apparent from these two figures that the network I simulating theline impedance, cannot absorb an appreciable amount of the telephonecurrents from the telephone 16 line because of the high impedanceoffered such currents by coils Lz nor can it absorb an appreciableamount of energy from the telegraph circuit because of condensers C3.

From Fig. 3 it is apparent that the conditions 20 for balance of thebridge circuit are that L1==Le and 03:04. For satisfactory operation theimpedance of the bridge, which is equal to the impedance of one of itsfour equal arms, should equal the impedance of the lines connecting 25thereto.

The bridge of this invention may be considered as a device forinterconnecting two pairs of circuits so that the circuits of each pairwill be conjugate and so that transmission to and from either circuit ofone pair employing currents of diiferent frequencies, for example,telephonetelegraph circuits, will tend to be excluded from a particularcircuit, viz. the balancing network circuit, of the other conjugatepair. This re-- sults in more efficient operation than with the usualdevices of the prior art in which these currents divide equally betweenthe transmission line and the balancing network.

For perfect balance of the bridge of this invention the line .andbalancing network impedances should be equal and the impedances of thetwo communication circuits should be equal. In practice these impedancesneed be only reasonably well matched for satisfactory operation.

It is to be understood of course that the arrangement shown in thedrawing and described hereinbefore is purely diagrammatic andillustrative of the principle involved and that the invention is'capable of embodiment in different forms without departing from thespirit of the invention and the scope of the appended claims.

What is claimed is:

-1. Static means for interconnecting a transmission line with atelegraphic circuit and a telephone circuit, said means including a linebalancing network and a Wheatstone bridge, each arm of said bridgecomprising an inductance and a capacity in series, said arms beingconnected so 'that at each Junction of two arms of said bridge-aninductance of one arm connects with a capacity of the vother arm wherebyin addition to the usual balance and frequency discrimination betweenthe telegraphic and telephone circuits, discrimination against thedissipation of both telegraphic and telephone currents in the linebalancing network is obtained.

2. Static means for interconnecting a transmission line with twocommunication circuits employing currents of different frequencies, saidmeans including a line balancing network and a Wheatstone bridge eacharm of said bridge comprising a plurality of unlike reactances inseries, said arms being connected so that at each junction of two armsof said bridge, unlike reactances are connected together whereby inaddition to the usual balance and frequency discrimination between saidtwo communication circuits, discrimination against the dissipation ofcurrents of both circuits in the line balancing network is obtained.

3. Static means for interconnecting two pairs of circuits, the circuits01 each pair being made conjugate through said means, the circuits ofthe first of said pairs being designed to transmit and receive currentsof different frequencies, said static means including a Wheatstonebridge each arm of said bridge comprising an inductance and a capacityin series, said arms being connected so that at each junction of twoarms of said bridge an inductance of one arm connects with a capacity ofthe other arm whereby, in addition to the usual balance and frequencydiscrimination between the circuits of said first pair, discriminationagainst the dissipation of currents of both said first pair of circuitsin a particular circuit of said second pair is obtained.

FRANK AUGUSTUS COWAN.

